1. Field of the Invention
The present invention relates to a method of epitaxially growing a GaN semiconductor layer on a highly lattice mismatched substrate.
2. Description of the Prior Art
The epitaxial growth of a semiconductor on a highly mismatched substrate results in extremely strained semiconductor layers. This strain gives rise to the formation of many extended defects such as dislocations, grain boundaries, stacking faults, inversion domains, and is generally responsible for the poor quality of grown semiconductor layers. Buffer layers have been used for several decades for strain reduction and improving the quality of grown semiconductor layers. Usually, buffer layers are made of solid polycrystalline or amorphous semiconductors. Such buffer layers allow the elimination of up to 90% of the strain.
It is an object of the present invention to provide a growth method that allows the substantial elimination of the strain resulting from high mismatch between the lattice parameters of a semiconductor and a substrate on which the semiconductor is grown.
According to the present invention, there is provided a method of epitaxially growing a GaN semiconductor layer on a highly mismatched substrate using a buffer layer with a solid-liquid phase transition comprising:
the epitaxial growth on the substrate of the buffer layer at a temperature lower than the melting temperature of the buffer layer;
the epitaxial growth on the buffer layer at a temperature lower than the melting temperature of the buffer layer of a protective layer with a melting temperature higher than the growth temperature of the GaN semiconductor layer to be epitaxially grown; and
the epitaxial growth on the protective layer at a temperature higher than the melting temperature of the buffer layer of the epitaxial GaN semiconductor layer with a thickness greater than the thickness of the protective layer.
The growth of the epitaxial GaN semiconductor layer occurs on the thin protective layer which maintains the flatness of the liquid buffer layer and protects it from formation of liquid droplets on the substrate surface.
Since the protective layer is thin and weakly mechanically coupled to the substrate via the thin liquid buffer layer, it serves as a compliant substrate for the epitaxial GaN semiconductor layer.
Thus, the use of a buffer layer with solid-liquid phase transition allows the growth of high quality strain-free epitaxial semiconductor layers on highly mismatched substrates.
The buffer layer could be one of a metal, a metal alloy, a semiconductor alloy, a metal-semiconductor alloy and an ionic crystal of groups I-VII or II-VI.
The buffer layer could be one of Al, Cu, Mg, Pb, Au, Ag and their alloys, the substrate being one of sapphire and SiC.
The buffer layer could be one of Al, Cu, Mg, Pb, Au, Ag and their alloys, the substrate being one of sapphire and SiC.
The protective layer could be one of MgO, Al2O3, AlN, GaN, InN and their alloys, the substrate being one of sapphire and SiC and the buffer layer being one of epitaxial AlN, GaN, InN and their alloys.
The buffer layer preferably has a thickness from 5 xc3x85 to 500 xc3x85.
The protective layer preferably has a thickness from 5 xc3x85 to 500 xc3x85.